And little bugreport. With the latest patch (and without) when reading PDF in ladnscape mode, in scroll mode, there is an error of dotted line placement — sometimes it just disappears, somtimes placed incorrectly & only in a rare cases it's just where i've done reading on the previous page.

I think it should work as you describe by design.

1) The dotted lines disapear if you are in middle sections of page. (They are virtually at the beggining and end of screen)
2) Dotted lines do not have meaning to show where you were before. They mean, where the viewport will move if you press Next/Prev.

So, generally, dotted lines show only if you are close to botttom or top of the page.

At least, this is my understanding, how it works.

@Booxtor
It might be a good idea draw the lines only on the left and right margin of screen. One or 2 centimeters will do. Some readers do not like the margin. This way, it would give the information and would not obstruct the text.

Also might be good to show the "direction" - distinguish upper margin and lower margin. I would suggest triangles directed up (or upside down T) for bottom of future viewport and triangles directed down (or T) for top of viewport.

It would be more clear how the viewport will be placed after the movement. Also if viewport position and zoom combination creates situation that two margins are displayed, one does not have any clue to which margin the movement will lead. If I move up the viewport may move to lower or upper margin. Which one depends on zoom.

And also vertical lines/marks would be handy (again with direction info - left/right triangles or Ts or line + parrelel & dotted line)